class instrumenet(object):
    def make_sound(self):
        pass
class piano(instrumenet):
    def make_sound(self):
        print('钢琴正在演奏')
class urheen(instrumenet):
    def make_sound(self):
        print('二胡正在演奏')
class violin(instrumenet):
    def make_sound(self):
        print('小提琴正在演奏')
class bird():
    def make_sound(self):
        print('小鸟在唱歌')
def play(instrument):
    instrument.make_sound()
if __name__ == '__main__':
    play(piano())
    play(urheen())
    play(violin())
    play(bird())